For example, in a projector for image display, such as a DLP™ projector and a liquid crystal projector, and a photomask exposure apparatus, a high intensity discharge lamp (an HID lamp) such as a xenon lamp and a super-high pressure mercury lamp has been used. As an example, a principle of a projector is described using FIG. 6 (see JP-A-2004-252112, etc.). FIG. 6 is a view for explaining one embodiment of a portion of one type of conventional projector according to the projector of the present invention.
As described above, light from a light source (SjA) formed of a high intensity discharge lamp or the like enters an incident end (PmiA) of light uniformizing means (FmA) with the help of focusing means (illustration thereof is omitted) formed of a concave reflector, lens, or the like, and the entering light is output from an emission end (PmoA). Here, for example, an optical guide may be used as the light uniformizing means (FmA). The optical guide is also called by a name such as a rod integrator or a light tunnel, and may be constituted of a rectangular cylinder formed of a light transmissive material such as glass or resin. Light input to the incident end (PmiA) propagates inside the light uniformizing means (FmA) while repeatedly being totally reflected by side faces of the light uniformizing means (FmA) in accordance with a principle the same as that of an optical fiber. This achieves a function of sufficiently uniformizing illuminance on the emission end (PmoA) even when distribution of the light input to the incident end (PmiA) is non-uniform.
Incidentally, regarding the optical guide described above, in addition to the above-described optical guide constituted of a rectangular cylinder formed of a light transmissive material such as glass or resin, there is an optical guide which is constituted of a hollow rectangular cylinder having inner faces being reflectors, causes light to propagate therein while, similarly, repeatedly reflecting the light with the inner faces, and thereby achieves a similar function.
An illumination lens (Ej1A) is disposed so that a square image of the emission end (PmoA) is formed on a two-dimensional light amplitude modulation element (DmjA), whereby the two-dimensional light amplitude modulation element (DmjA) is illuminated with the light output from the emission end (PmoA). However, in FIG. 6, a mirror (MjA) is disposed between the illumination lens (Ej1A) and the two-dimensional light amplitude modulation element (DmjA). Then, the two-dimensional light amplitude modulation element (DmjA) directs the light to a direction entering an image projection lens (Ej2A) for each pixel, according to a video signal, or the two-dimensional light amplitude modulation element (DmjA) modulates the light to direct the light to a direction not entering the image projection lens (Ej2A) for each pixel, and, thus, to display an image on a screen (Tj).
Note that the two-dimensional light amplitude modulation element as described above is also called light bulb, and in the case of the optical system of FIG. 6, DMD™ (Digital micro-mirror device) is generally often used as the two-dimensional light amplitude modulation element (DmjA).
Regarding the light uniformizing means, in addition to the above-described optical guide, there is light uniformizing means called a fly eye integrator. As an example, a principle of a projector using this light uniformizing means is described using FIG. 7 (see JP-A-2004-142141, etc.). FIG. 7 is a view for explaining one embodiment of a portion of one type of conventional projector according to the projector of the present invention.
Light from a light source (SjB) constituted of a high intensity discharge lamp or the like enters, as substantially parallel luminous flux, an incident end (PmiB) of the light uniformizing means (FmB) formed of a fly eye integrator with the help of collimator means (illustration thereof is omitted) formed of a concave reflector, lens, or the like, and the entering light is output from an emission end (PmoB). Here, the light uniformizing means (FmB) is configured by combination of a front fly eye lens (F1B) on incident side, a rear fly eye lens (F2B) on exit side, and an illumination lens (Ej1B). Each of the front fly eye lens (F1B) and the rear fly eye lens (F2B) is formed by vertically and horizontally arranging many square lenses having the same focal length and the same shape.
Each of the front fly eye lenses (F1B) and the corresponding lens of the rear fly eye lens (F2B) on the rear stages of the corresponding front fly eye lenses constitute an optical system called a Kohler illumination optical system, and thus, many Kohler illumination optical systems are arranged vertically and horizontally. Typically, Kohler illumination optical system is constituted of two lenses. When this optical system collects light with a front lens to illuminate a target surface, the two lenses are disposed so that the front lens forms a light source image not on the target surface but on a surface of a center of a rear lens, and the rear lens forms an image of a square of an outer shape of the front lens on the target surface (a surface desired to be illuminated), whereby the target surface is uniformly illuminated. The action of the rear lens is to prevent phenomenon occurred in a case where the rear lens is not provided, when the light source is not a complete point light source and has a finite size, illuminance in the periphery of the square on the target surface is dropped depending on the size. The rear lens allows uniform illuminance over to the periphery of the square on the target surface without depending on the size of the light source.
Here, in the case of the optical system in FIG. 7, since substantially parallel luminous flux basically enters the light uniformizing means (FmB), the front fly eye lens (F1B) and the rear fly eye lens (F2B) are disposed so that a distance therebetween becomes equal to the focal length thereof, and thus, an image on the target surface of uniform illumination as Kohler illumination optical system is generated to the infinity. Incidentally, since the illumination lens (Ej1B) is disposed on a rear stage of the rear fly eye lens (F2B), the target surface is drawn on a focal plane of the illumination lens (Ej1B) from the infinity. Each of the many Kohler illumination optical systems arranged vertically and horizontally is parallel to an incident optical axis (ZiB), and luminous flux enters each of the Kohler illumination optical systems substantially axisymmetrically to the center axis thereof. Therefore, output luminous flux is also axisymmetrical. Accordingly, images of the outputs of all of the Kohler illumination optical systems are formed on the same target surface on the focal plane of the illumination lens (Ej1B) by property of the lens in which light beams entering a lens surface at the same angle are refracted to travel toward the same point on the focal plane irrespective of incident positions of the respective light beams on the lens surface, namely, Fourier transform function of the lens.
As a result, illumination distributions on the respective lens surfaces of the front fly eye lenses (F1B) are all overlapped, and thus a synthesized square image whose illuminance distribution is more uniform than that in the case of one Kohler illumination optical system, is formed on the incident optical axis (ZiB). When the two-dimensional light amplitude modulation element (DmjB) is disposed on the position of the synthesized square image, the two-dimensional light amplitude modulation element (DmjB) serving as an illumination target is illuminated with light output from the emission end (PmoB). Incidentally, in the illumination, a polarization beam splitter (MjB) is disposed between the illumination lens (Ej1B) and the two-dimensional light amplitude modulation element (DmjB) to reflect the light toward the two-dimensional light amplitude modulation element (DmjB). Then, the two-dimensional light amplitude modulation element (DmjB) modulates the light and reflects the modulated light such that the polarization direction of light for each pixel is rotated by 90 degrees or is not rotated, according to a video signal, whereby only the rotated light passes through the polarization beam splitter (MjB) and enters an image projection lens (Ej3B), thereby displaying an image on the screen (Tj).
In the optical system in FIG. 7, LCOS™ (silicon liquid crystal device) is commonly often used as the two-dimensional light amplitude modulation element (DmjA). In such a liquid crystal device, since only a component of light in a specified polarization direction is effectively modulated, a component of light parallel to the specified polarization direction is normally transmitted without being modulated. However, a polarization aligning function element (PcB) that rotates polarization direction of only a component of light perpendicular to the specified polarization direction by 90 degrees and consequently allows all of light to be effectively used may be interposed, for example, on a rear stage of the rear fly eye lens (F2B). In addition, for example, a field lens (Ej2B) may be interposed immediately before the two-dimensional light amplitude modulation element (DmjB) so that substantially parallel light enters the two-dimensional light amplitude modulation element (DmjB).
Incidentally, regarding a two-dimensional light amplitude modulation element, in addition to the reflective two-dimensional light amplitude modulation element illustrated in FIG. 7, a transmissive liquid crystal device (LCD) is used to have an optical arrangement adopted therein (see JP-A-10-133303, etc.).
Incidentally, in a typical projector, to perform color display of an image, for example, a dynamic color filter such as a color wheel is disposed on the rear stage of the light uniformizing means to illuminate the two-dimensional light amplitude modulation element with color sequential luminous fluxes of R, G, and B (red, green, and blue), and color display is achieved time-divisionally. Alternatively, a dichroic mirror or a dichroic prism is disposed on the rear stage of the light uniformizing means to illuminate the two-dimensional light amplitude modulation element that is provided independently for each color, with light color-separated to three primary colors of R, G, and B, and a dichroic mirror or a dichroic prism is disposed to configure an optical system for performing color synthesis of the modulated luminous fluxes of the three primary colors of R, G, and B. However, to avoid complication, these are omitted in FIGS. 6 and 7.
However, the above-described high intensity discharge lamp has disadvantages such as low conversion efficiency from supplied power to optical power, that is, large heating loss, short life, or the like. As an alternate light source overcoming these disadvantages, a solid light source such as an LED and a semiconductor laser has attracted attention in recent years. Among them, in the LED, as compared with the discharge lamp, the heating loss is small, and the life is long. However, since light emitted from the LED does not have directivity similarly to the discharge lamp, there is a problem that usage efficiency of light is low in an application capable of using only light in a certain direction, such as the above-described projector and an exposure apparatus.
On the other hand, the semiconductor laser has a disadvantage that speckle occurs due to high coherency, but the disadvantage is overcome by various technical improvement such as usage of a diffuser plate. In the semiconductor laser, similarly to LED, the heating loss is small, the life is long, and in addition, the directivity is high. Therefore, the semiconductor laser has an advantage that usage efficiency of light is high in the application capable of using only light in a certain direction, such as the above-described projector and an exposure apparatus. Moreover, in the semiconductor laser, optical transmission can be performed with high efficiency through an optical fiber while utilizing the high directivity, and therefore, the installation position of the semiconductor laser can be separated from the position of a projector or the like using the light, so that flexibility of device designing can be enhanced.